Method of producing a collagen strand



E. J. GRISET ETAL METHOD OF PRODUCING A COLLAGEN STRAND Dec. 17, 1963 13 Sheets-Sheet 1 Filed Oct. 4. 1961 Dec. 17, 1963 E. J. GRISET ETAL METHOD OF PRODUCING A COLLAGEN STRAND Filed 0013. 4. 1961 13 Sheets-Sheet 2 QMUJMLLL Dec. 17, 1963 E. J. GRISET ETAL METHOD OF PRODUCING A COLLAGEN STRAND Filed Oct. 4. 1961 13 Sheets-Sheet 3 E. J. GRlsET ETAL 3,114,593

METHOD oF PRoDUcING A coLLAGEN STRAND Dec. 17, 1963 Filed Oct. 4, 1961 15 Sheets-Sheet 4 @gw @Mm Dec. 17, 1963 E. J. GRlsET ETAL METHOD oF PRoDucING A coLLAGEN STRAND 13 Sheets-Sheet 5 Filed Oct. 4, 1961 Dec. 17, 1963 E. J. GRlsET ETAL.` 3,114,593

METHOD oF PRoDUcING A coLLAGEN STRAND Filed Oct. 4, 1961 l5 Sheets-Sheet 6 KMA-MM Dec. 17, 1963 E. J. GRlsET ETAL 3,114,593

METHOD 0F PRODUCING A COLLAGEN STRAND Filed Oct. 4. 1961 15 Sheets-Sheet 7 T1 :'.IL l T1 -12- me/whom QMJLLL;

Dec. 17, 1963 E. J. GRlsl-:T ETAL 3,114,593

METHOD 0F PRoDUcING A COLLAGEN STRAND Filed oct. 4. 1961 13 SheetS-Shee'b 8 Dec. 17, 1963 E. J. GRlsET ETAL 3,114,593

' METHOD oF PRoDUcING A COLLAGEN STRAND Filed oct. 4, 1961 1s sheets-sheet 9 Dec. 17, 1963 E. J. GRlsET ETAL 3,114,593

METHOD OF' PRODUCING A COLLAGEN STRAND Filed 0011. 4, 1961 13 Sheets-Sheet l0 @f Wm Dec. 17, 1963 E. J. GRISET ETAL METHOD 0F' PRODUCING A COLLAGEN STRAND Filed 0G13. 4, 1961 13 Sheets-Sheet l1 T 1 CIZEL De@ 17, 1963 E. J. GRISET ETAL 3,114,593

METHOD 0F PRODUCING A COLLAGEN STRAND Filed 001'.. 4. 1961 13 Sheets-Sheet' l2 SMQ/WIM w -QMJ-wl Dec. 17, 1963 E. J. GRISET ETAL 3,114,593

METHOD OF PRODUCING A COLLAGEN STRAND Filed Oct. 4, 1961 13 Sheets-Sheet 13 2M @om vm United States Patent O 3,114,593 METHD F PRDUCHNG A COLLAGEN STRAND Ernest l. Griset and Thomas L. Reissmann, Bound Broch, and Joseph Nichols, Princeton, NJ., assignors to Etlricon, lne., a corporation of New Jersey Filed Get. 4, 196i, Ser. No. 142,934 ll Claims. (Cl. 18-54) 'Ilhis invention relates 'to new and useful methods for producing a new and improved collagen strand by con- 4tinuous extrusion. The products of the present invention are particularly adapted to be utilized `as absorbable sutures and ligatures.

Practically the entire production of absorbable sutures and ligatures is currently made from sheep or beef gut by a process that is both time consuming and expensive, but the current method of manufacture is not adapted to produce a uniform product. The percent of production that is rejected, therefore, for some defect such as 'lack of tensile strength and lack of uniformity, is large. The starting material, e.g., sheep intestines, is available only in limited quantities and one can not predetermine the size of the finished product.

There are also inherent defects in the best obtainable sutures made from gut. The individual sutures may vary widely in cross-section and the length of such a sut-ure is limited by the length of the intestinal material processed. lFurthermore, `.a gut suture rwill become brittle and decrease in ilexibility and strength on aging if fats and other contaminants are not completely eliminated during processing.

In View of the obvious deiciencies of surgical catgut and the disadvantages of the present method of manufacture, many attempts have been made to make a better prod-uct from other sources of collagen. Collagen is present in all connective tissue and may be conveniently obtained from hides and tendons. Three dilferent routes to the preparation of surgical sutures from such collagen sources have been investigated.

By one process, ie., that of Salo U.S. Patent No. 2,598,608, the collagen is Worked up into a swollen librous mass and the collagen solids are precipitated, washed, redispersed by the addition of an acid such as rnalonic acid and extruded through a nozzle into a dehydrating bath.

A second process of preparing surgical sutures from non-intestinal collagen, eg., that of Cresswell U.S. Patent No. 2,637,321, involves dissolving the collagen in a solvent and subsequently regenerating it by extruding the solution into a coagulating bath.

A third method, e.g., that of Weaver U.S. Patent No. 505,148 shreds animal tendon to produce woolor cottonlike fiber and then spins the dry liber into threads.

`All of these methods, however, attempted to extrude or shape collagen at high concentrations, Le., of the order of 2-l5% by Weight. ln preparing such concentrated masses of collagen, much of the collagen is degraded by mechanical treatment and the action of acid solutions at elevated temperatures. Moreover, the collagen masses so obtained are extremely viscous or paste-like, and the alignment of individual collagen libers necessary for optimum tensile strength is difficult to accomplish.

DEFlNlTIONS lor the sake of clarity, the terms used herein are defined as follows:

The term swollen collagen fibril, las used herein, means a thread-like collagen structure that has been swollen in `.acid solution to a diameter of about 5,000 to about 90,000 Angstrom units.

Patented Dee. i7, i953 The term m0nolament, as used herein, means a single thread of oriented collagen fibrils as extruded through a single orifice in a spinnerette.

The term multililament as used herein, means a group of individual separate collagen filaments extruded through a spinnerette.

The term tape, as used herein, means a group of individual monolilaments that have been united to form a unitary structure that is ribbon-like in shape.

Fflhe term strandj las used herein, means a group or individual nronoilaments that have been united to form a unitary structure of circular cross-section.

In accordance with the present invention, it has now been discovered that an extremely strong collagen strand may be produced from a homogeneous dispersion of swol-len collagen fibrils having a solids content much lower than heretofore used, i.e., of the order of 0.73 percent to 0.82 percent. Collagen strands formed by extrusion from a relatively low solids dispersion of collagen iibrils will produce sutures which possess excellent Wet strength characteristics and are very strong when dry.

The utilization of a homogeneous collagen dispersion having the low solids content indicated above and in which the collagen material has been reduced to particles of iilbrillar size introduces diliicult problems in treating and handling the `extruded lilament from the momen-t it leaves the oriiice of the `spinnerette until it has been coalesced with other filaments and dried to the ultimate size in Which it is to be later used. Thus, the extrusion of such a low solids material produces an exceedingly fragile liamen-t which must be handled with the greatest delicacy `and care during the subsequent treatments in which it is coagulated, stretched, while still wet, twisted, tanned, plasticized, cohered kand dried.

When the mass of swollen collagen fibrils leaves the spinnerette orifice, it is essentially a liquid which must immediately be given a coagulating treatment in order to preserve the shape imparted to the liquid as it leaves the mouth of the spinnenette and is still traveling under the kinetic energy imparted by the extrusion force. Once this initial coagulation takes place, the extruded multilament possesses tangible form and integrity of its own, but nevertheless remains weak, fragile and subject to breaking as it passes in the wet state through subsequent conditioning treatments. in spite of its fragile nature, the exacting requirements of continuous production are such that this initially wet multiiilament must be slowly dried under such conditions that as the solids content of the multiilament increases, the ratio of .water to coagulant increases. It is necessary that the collagen multirilament be wet as it is squeezed, stretched and twisted if the individual monolaments are to cohere to form the desired tape or strand. lf too much moisture is present, the collagen multiiilarrient will not cohere to form a tape or strand. Proper control may be provided by careful selection of the coagulant and the presence of cosolvents in the dispersion of collagen fibrils. The volatility of the coagulant and cosolvent should be such that the ratio of coagulant to water present in the multiiilament decreases slowly until such time as the total collagen solids content Iis sufficiently high to provide the necessary tensile strength. The recognition and solution of these processing difliculties and the provision of apparatus for carrying out the requisite treatment steps cornprise some of the foundations of the present invention.

OBJECTS -lt is lan object of the invention to extrude a satisfactory suture material.

It is -another object of the present invention to extrude 3 a pure and ho-mogeneous dispersion of swollen collagen fibrils into a dehydrating bath to produce a multiiilament, the individual monofilaments of which may be united to form a continuous strand of cohered par-allel monoiilaments having unusual physical properties.

iIt is also an object of this invention to produce shaped articles of collagen suitable for surgical use by continuously `extruding a dispersion of swollen collagen fibrils into a dehydrating bath.

It is a further object of this invention to produce a continuous unitary strand from parallel monofilaments of oriented collagen fibrils having characteristics superior to surgical sutures derived from gut.

The objects of this invention may be realized by extruding a homogeneous dispersion of pure swollen coll-agen fibrils into a dehydrating bath to form multifilament. The multiilament may be further processed, for example, by wetting out, washing, tanning, twisting and stretching in proper sequence to obtain a strand or tape of uniform diameter and physical properties. iIn the practice of the present invention, therefore, a dispersion of swollen collagen :fibrils is extruded to form continuous filaments in which the individual collagen brils are oriented parallel to the major axis of the filament. The multifllament is then further processed to form a rounded strand of parallel monoiilaments having a uniform cross-section. The extrusion and spinning operations require a special technique designed for this specific purpose.

The basic raw material entering into the manufacture of extruded collagen sutures by the present process consists of a dispersion of swollen collagen fibrils which may originate in different animal species or in different tissues within a single species. These collagen fibrils are characterized by having a uniform diameter, a periodic crossbanding measuring about 640 Angstroms per unit and the ability to swell reversiibly in aqueous acid solution. Collagen fibrils from beef leg tendon are preferred for the present process.

It is important in preparing `a dispersion of swollen collagen fibrils suitable for extrusion yand spinning that the removal of impurities naturally present in mammalian tendon, and the separation of the longitudinally arranged fibrils to form a homogeneous dispersion, be effected under conditions that avoid solution or degradation of the collagen fibrils. The tensile strength of the extruded product is dependent upon retaining the original collagen fibrils structure.

In the spinning process, the homogeneous dispersion of swollen collagen fibrils is extruded into a ketone dehydrating bath through a spinnerette which orients the individual collagen fibrils in a direction parallel to the direction of extrusion. it has been postulated that the ultimate strength of the extruded filament is related to the lateral bonds between collagen fibrils. Thus, a parallel alignment of the inidvidual fibrils is highly desirable as such an arrangement will provide the maximum number of lateral bonds, and the maximum tensile strength.

The extruded filaments are stretched to further orient the collagen fibrils and may be collected as a multifilament or cohered to form a tape or strand. The nature of the product obtained (multifilament, tape or strand) will depend upon the spinning process employed.

-In the direct spinning process, the multifiliament from the dehydrating bath may be wet out, stretched, twisted, tanned and then stretched `and twisted a second time while still wet with the tanning solution. This process gives ya collagen strand that may be used as an absorbable suture. Such collagen stnands have a tensile strength, knot strength, and flexibility that is equivalent to that of sutures made from sheep intestines.

In the indirect spinning process, the multifilament from the dehydrating bath is not wet o-ut prior to stretching and drying. The multifiiament is stored as such or as tape. The number of individual filaments in the multifilament or tape will determine the diameter of the final Cil 4 strand. Thus, the indirect spinning process is convenient for manufacturing sutures of different sizes, and particularly large size sutures.

It will be understood that the foregoing general description 'and the following detailed description as well are exemplary and explanatory but are not restrictive of the invention.

DRAWINGS Referring now in detail to the present preferred embodiment of the invention, illustrated by way of example in the accompanying drawings:

Fl URE 1 is a flow diagram illustrating the sequence of steps in preparing a dispersion of pure collagen fibrils from animal tendon.

FIGURE 2 is a drawing of a preferred source of collagen-the deep fiexor tendon as obtained from cattle.

FIGURE 3 is a sectional view of a kettle that is used to prepare a homogeneous dispersion of collagen fibrils.

FGURE 4 is a sectional view of the dispersion liettle along the line 4 4 of FIGURE 3.

FIGURE 5 is a perspective view of a take-up spool for a dried strand.

FGURE 6 is a side elevation of a section of a spinning mac ne and shows an extrusion pump in series with a reservoir for the fibril dispersion, homc-genizing iets and a screen filter.

FGURE 7 is a detailed sectional view of the homogenizing jets that are associated with the spinning niachine of FGURE 6.

FIGURE 8 is an exploded View of a screen filter of the type used to remove non-swollen material from the colla-gen dispersion.

FEGURE 9 is a schematic view of a spinning machine that may be used in the manufacture of continuous collagen strands by the direct spinning process.

yEIGURE 10 is a side elevation, partially in section, of a spinnerette arranged for the horizontal spinning of collagen muhifilaments or strands. This figure aise illustrates the circulation of the dehydrating bath.

FEGURE ll is a side elevation, partially in section, of a spinnerette and the associated dehydrating bath arranged for vertically downward spinning.

FIGURE l2 is a detailed sectional view of a spinnerette and the associated spinning column and dehydrating bath arranged for vertically upward spinning.

*IGURE 13 is an inverted plan view of an improved spinnerette.

FEGURE 14 is a sectional view of the spinnerette taken on the line 14-14 of FIGURE 13.

FiGUEE l5 is a plan view of the spinnerettc illustrated in FIGURE 13.

FiGURE 16 is an enlargement of a portion of FIG- URE 14 that better illustrates the taper of thc spinner-ette orifices.

FiGURE 17 is a sectional view of a different type of spinnerette in position yfor vertically upward spinning.

FGURE 18 shows a modification of the spinncrette illustrated in FIGURE 17.

FIGURE 19 is an enlarged sectional view of the spinnerette taken on the line iii-i9 of FIGURE 18.

FiGURE 20 is a side elevation, partially in section, of a spinnerette and spinning tube illustrating the associated spin bath, and means for maintaining the coinposition of the spin bath constant.

FGURE 211 is a `detailed perspective view of a part of the spinning machine showing ti e Godet Ml which taires up the strand from tne dehydrating bath. This figure also shows the idler 3.624 which is associated with the godet lill.

FEGURE 22 is a side elevation of the idlcr trated in FIGURE 2l.

FGURE 23 is a per ctive view of the tanning sec-y tion of the spinning machine and illustrates one method. of continuously tanning the moving strand.-

illus-y FlGURE 24 is an end view of the idler pulley 1li-5 of FIGURE 23 with the tanning bath in position.

FIGURE 25 is a perspective view of a 'false twister which is used to round the strand and `dry the strand during the spinning process.

FGURE 26 is an enlarged view illustrating the leature of the false twister of FlGURE 25 which facilitates threading the spinning machine.

FIGURE 27 is a sectional View of the false twister illustrated in vFIGURE 26.

FlGURE 28 is a schematic view or a spinning machine that may be used in the manufacture of con-tinuous collagen tape; and

FIGURE 29 is a schematic view of a machine that may be used in the manufacture of collagen strands from collagen tape in the indirect spinning process.

To assist in a bet-ter understanding or the present invention, the speciiication will be divided into two sections. The viirst part of the specification will relate to preparing. a dispersion of pure swollen collagen fibrils suitable for extrusion, which forms no part of the present invention. The second part of the specification will describe a method of and apparatus for continuously spinthe pure collagen dispersion which constitutes the present invention.

THE CGLLAGEN DlSPE-RSlON The general sequence of operations in the formation of a dispersion of pure swollen collagen fibrils suitable for extrusion is shown in -FlGURE l. By the process to be described, one may dis-perse the native collagen iibrils and remove impurities therefrom without such denaturation or degradation of the collagen as would reduce the tensile strength of the iinal strand.

The raw material for the articles of this invention is mammalian tendon. Whales are a lar-ge source of collagen and wha-1e tendon collagen .is a satisfactory startmaterial. Pork, sheep and beef tendon are also satisfactory.

The various sections of bovine tendon are illustrated in .FIGURE 2. ln this ligure, certain sections of the tendon have been arbitrarily designated by the letters A through n Fl'he A portions consist of sheaths (Annular Ligaments) which surround the two C sections. The A portions are also connected directly to the B tendon (the superficial ilexor tendon). The C material consists of two small dense shanlcs which branch oli the larger D section. These C sections `(branches or the deep ilexor tendon) contain a larger percentage of material that does 4not swell in acid solutions. That section of the single shank identified by the letter D" Iin FIGURE 2 (the deep iiexor tendon) is the preferred portion of the tendon for preparing the collagen dispersion to be "escribed, but the E portion may also be used.

'vl/ith reference to FIGURE l, the beef tendon (preferably the deep liexor tendon) is received yfrom the packing house in frozen condition to prevent deterioration and is thawed to permit cleaning the tendon of Ifat, non-collagenous protein and other extraneous matter. The cleaned tendon is then Ifrozen in bundles resembling stacks or" cordwood and sliced to a thickness of about l() to 25 mils. Thiclrer slices swell slowly in aqueous acid solutions and are idimcult to disperse. rl'liinner slices disperse readily, but the dispersion when extruded has poor tensile strengtl. Preferably, the .tendon is slice across the major axis as lengthwise slicing seems to result in slower swelling.

The sliced tendon is next treated with an enzyme solution to dissolve the elastin which encircles and ties together the native collagen fibers. By this treatment, substantially all of the elastin is dissolved and can be removed. Most of the fats present also separate out in this process. Proteolytic enzymes from either plant or animal sources may be employed to advantage. Pancreatin is an enzyme that is eiiective in removing elastin.

Enzymes derived from plants, such as ficin, are also useful. Another enzyme that will perform this function is one prepared by extracting commercial malt diastase (U.S.P. IX) with water. The tendon-enzyme mixture is stored at room temperature for l5 to 20 hours. By this treatment, substantially all of the elastin is separated from the native collagen fibers.

After the enzyme treatment, the tendon slices are washed with water. Soluble protein and lipids may be removed by treating the slices with a dilute aqueous solution of a chelating agent, such as ethylenediaminc tetrasodium tetraacetate. Following this treatment, the tendon slices are washed again to remove residual traces of the chelating agent.

The cleaned tendon slices at this point contain a hivh percentage of purified collagen associated with material that does not swell in an acid solution. The next step is to swell this collagen in an acid solution to form a homogeneous dispersion or" collagen fibrils, but it is most important during this swelling step that the collagen slices not be permitted to cohere. As collagen swells, it becomes sticky, and, if the individual collagen slices are permitted to stick together, the interior of the resulting mass will not have contact with the swelling solution. Therefore, it is desirable to prevent coherence of the individual tendon slices in order to obtain a homogeneous libril dispersion in a practical time. A dispersion kettle (see FIGURES 3 and 4) having an eccentric paddle 1% is used to minimize lump entanglement.

In the dispersion kettle, the collagen slices areslowly stirred in an acid solution by the eccentric paddle, allowing the collagen slices to absorb the acid solution with swelling,

Temperature becomes a critical factor after addition of acid to the tendon slices as the collagen is degraded in the presence oi acids at about 30 C. and above. For this reason, all processing subsequent to the acid addition should be carried out at temperatures below about 25 C.

The swelling solution may be an aqueous solution containing cyanoacetic acid. The amount of acid present will vary with the equivalent weight of the acid and its ionization constant. In general, however, an acid content of about 0.20 percent to about 1 percent of the total weight of the solution is used. The preferred pH is 2-3.

lt is reasonable to expect that with increasing solids content, a situation will eventually be reached wherein all of the available swelling iiuid would be soaked up and bound in the collagen fibrils. The dispersion of swollen tendon collagen librils is believed to undergo a transition from a two-phase (free fluid plus swollen fibrils) to a one-phase (swollen fibrils) system at a solids concentration of about 0.73 percent to 0.82 percent. As the concentration of collagen is `increased above 0.82 percent by weight, the free l'luid in the continuous phase of the dispersion is imbibed by the swollen collagen fibrils and a one-phase system consisting only of swollen collagen fibrils is formed.

Thus, increasing the collagen concentration (above about 0.82 percent) results simply in a mass of swollen collagen fibrils. Such swollen collagen masses have an extremely high viscosity. When the collagen dispersion is to be used to extrude filaments, the amount of collagen solids present in the swelling solution is preferably about 0.80 percent. A dispersion of collagen fibrils that has a solids content below 0.7 percent is diiicult to spin. On the other hand, a concentration of collagen iibrils greaterthan 0.82 percent results in a collagen mass that is very diiiicult to extrude. Of equal importance is the diiliculty in obtaining and maintaining a homogeneous starting material when the total solids are too high. It is extremely important that a collagen iibril dispersion which is to be extruded be homogeneous, as a small change in the solids concentration of the material being extruded will result in large cross-sectional variations in the final product.

Alter most of the swelling has taken pla e in the dispersion kettle (FlGURE 3), the suspension is homogenized by repeated passes through a stainless steel rotary metering pump` E67 modihed by milling 0.033 inch from the circumference of the gear teeth, and two stainless steel series-connected jets 08 and lll@ returning to the kettle through conduit 11G. The internal structure of these jets is illustrated by FIGURE 7.

rhe dispersion after homogenization still contains areolar connective tissue, blood vessels of the tendon and other unswollen non-collagenous material which would clog the spinnerette and must be removed. This is most readily accomplished by forcing the dispersion under pressure through a leaf filter, such as shown in FGURE S, which retains the non-collagenous material.

The dispersion of collagen fibrils immediately after filtration may be termed a green dispersion because attempts to spin this pro-duct without aging result in eX- cessive breakage of the spun filament. However, if the dispersion stands for too long a time at room temperature, degradation of the collagen occurs and the dispersion, if too old, produces strands of infeior tensile strength. Under optimum conditions, the collagen dispersion is aged at room temperature (about 25 C.) for a period of about 24 hours, and then stored in the rcfrigerator at C. until required for spinning. The collagen dispersion may be kept in the refrigerator for 3 or 4 weeks prior to spinning.

The preparation of a dispersion of pure swollen collagen iibrils, according to the procedure outline above, is designed to eliminate all impurities, as any discontinuity will result in breaks in the monoiilaments during the spinning process. Even minute air bubbles will cause breaks in the monolilaments and it becomes necessary, therefore, to remove all air from the dispersion just prior to use. This may be conveniently accomplished by placing the dispersion, just prior to spinning, in a large vacuum desiccator and applying a vacuum (about 15 mm. of mercury) for 2 or 3 hours. The presence in the aqueous dispersion of a liquid having a low vapor pressure, such as methanol, assists in the removal of air bubbles. Methanol is a preferred cosolvent because of its low specic gravity. As much as 50 percent by volume of methanol may advantageously replace the water in the collagen dispersion. The use of larger amounts will introduce di'liculties in swelling the collagen fibrils and result in a dispersion that is diliicult to homogenize and extrude. An aqueous dispersion that contains no cosolvent would require a longer time to completely deaerate under vacuum and would have different spinning properties.

In order to avoid introducing extraneous air when transferring the dispersion from the desiccator to the spinning reservoir, the dispersion may be introduced into the bottom of the spinning reservoir by evacuating the reservoir as illustrated in FEGURE 1.

SPNNlNG THE COLLAGEN DISPERSON The collagen dispersion may be spun either vertically or horizontally.

FlGURE 10 illustrates a horizontal collagen spinning machine. For the purpose of our description, however, the spinning process will be described with reference to the vertically upward spinning machine illustrated in FlG- URE 9.

The machine to be described has been designed for the continuous direct spinning of a strand about 6.5 mils in diameter from an aqueous dispersion containing about 0.8 percent of pure swollen collagen fibrils, but it will be understood that modiiications to produce strands of diiierent diameter are well within the scope of this invention.

It will be noted that the collagen dispersion is forced through a lixed spinnerette into an enclosed system recirculating dehydrating bath. The ilaments are pulled vertically upward out or" the bath by godet lill, and are stretched between godet 1.01 and 102. Provision is made to continuously treat the moving monoiilaments with a liquid at godets lill and 102 as shown in FIGURES 2l and 23. Godet lll?) imparts additional stretch and orientation to the strand and false twisters i112 and ll?, which precede godets 102 and 103, respectively, round and dry the strand. T he tensiometers E42 and M3 measure tension on the strand. The total span between the spinnerette and the take-up spool is preferably about 20 feet, and the distance between the surface of the spinnerette and the level at which the filaments leave the dehydrating bath is preferably about 22 inches.

Referring now to FlGURE 6, which illustrates one method, a metering pump 115 may be used to pump the dispersion from the reservoir 1M to the spinnerette.

Gn leaving the pump 115 the dispersion is homogenized by passage through nozzles lll? and M6 connected in series. rl'hese nozzles are of the type illustrated in FlG- 7. The nozzle is attached to the inl-et side of a small leaf iilter liti which removes some of the remaining non-collagenous foreign particles that might otherwise enter the spinnerette. A panel-mounted gauge M9 is connected to the lter to record pressure changes.

in FlGURE l2 there is shown a detailed view of the spinning tube and the position of the spinnerette within the circulating spin bath. The spinnerette holder 129 is preferably machined from hard-rubber stock and is fastened to the glass cylinder 12) by a fitting of the same material.

The spinnerette may be a brass plate about 1% inches in diameter and 1A inch in thickness, and is illustrated in FlGURES 13, 14, l5 and 16. The spinnerette shown therein is drilled with 40 openings arranged in three concentric rings although the number and arrangement of the openings may be varied. Each opening to the spin bath is approximately 1.8 mils in diameter, and each opening has a 30 taper from this diameter, at a point 34 mils from the spinnerette surface, to a 3/32-inch opening at the bottom surface of the spinnerette, as shown in the enlarged sectional View of FIGURE 16.

A columnar stainless steel spinnerette having a 6-inch lead 5f:- to openings 18 mils in diameter, as shown in FlGURES 17, 18 and 19, can be substituted for the brass spinnerette described above. 1f this type of spinnerette is used, better circulation may be obtained by obstructing the central opening with a stopper or cork 123i, as illustrated in FIGURE 18.

The brass plate spinnerette, however, has the advantage of lower initial cost as well as lower maintenance cost. Moreover, when using the brass plate type of spinnerette, the dehydrating bath volume may be smaller, and less line pressure is required. This type of spinnerette is adaptable to downward spinning, and FIGURE 11 shows an alternate arrangement of the spinning column which permits downward spinning of the filaments. In FIGURE l1, the collagen dispersion enters through the conduit 50 and is extruded downwardly through the spinning column 122 into the dehydrating bath 51 which overilows through the tube 52. The dehydrating bath enters the spinning column at the top through conduit 53.

Referring now to FIGURE l2, the dehydrating bath enters the spinning tube from the side and below the spinnerette and llows up the spinning column 122 cocurrent with the extruded collagen 1.23. The spinning column preferably has an internal diameter of l/z inch, is 22 inches in length, and is liared outwardly at an angle of 20 to an internal diameter or" 11/16 inches at its lower end. The circulation rate of the spin bath within this column is generally about 850 cubic centimeters per minute, but may be increased to more than 1200 cubic centimeters per minute. A circulation rate of about 850 cubic centimeters per minute provides a rapid change of the bath and the upward flow helps to carry broken laments away from the spinncrette opening and up the column. A circulation rate as low as 50 cubic centimeters per minute, however, will provide a satisfactory change of the spin bath.

rl`he circulating system for the spin bath is illustrated in FIGURE 20. The spin bath is preferably circulated by a centrifuge pump 124 from reservoir 126 which may contain 4 liters of solution, originally made up by adding 0.8 milliliter of reagent grade ammonium hydroxide (28%-30% NH3) and 35 grams of water to 1 liter of fresh commercial acetone. The original water content of this commercial acetone is about grams per liter. For optimum results, the composition of the spin bath should be maintained as follows:

Acetone 1 liter. Ammonia 120 to 140 milligrams of NH3. Water 40 to 60 grams.

If less ammonia is present in the spin bath, the extruded filament is too soft when formed at the spinnerette orening and if too much ammonia is present in the bath, the filaments are brittle and can not be stretched to obtain the desired orientation.

The water present in the spin bath has the opposite effect, in that too much water will result in an excessively soft filament, and too little water will give a brittle lilament that can not be stretched. Thus, the ammonia present in the acetone bath will compensate to some extent for the water present and vice versa.

The composition of the spin bath is quite important since a feather-like growth may be formed at the spinnerette surface should the concentration of ammonia increase above 160 milligrams per liter. Any feathers that are formed will result in discontinuity and poor tensile strength in the dried and stretched strand. lf the ammonia concentration falls below 100 milligrams per liter, the extruded filaments are too soft and ditiiculty with breakage is experienced. The composition of the spin bath may be maintained relatively constant by adding to the spin bath from the make-up reservoir 127 from 2 to about 3 liters of dehydrating solution each hour. The make-up reservoir contains double distilled acetone, to which has been added 5 cubic centimeters per liter of aqueous ammonia (about 1400 to 1500 milligrams of NH3). The overflow 128 functions to maintain the total volume of the spin bath constant.

Referring now to FIGURE 9, the spun collagen is transported through the machine by three godets 1111, 1192 and 103, preferably of nylon, each of which is preferably 3 inches in circumference. Godet 101 is illustrated in FlGURE 2l and godet 1112 in FIGURE 23. Directly below godet 1111 is an auxiliary nylon roller d, as shows in FIGURE 21. The separation of the strands on godet 1l1 is controlled by moving the axis of the auxiliary roller 104- with respect to the axis of the godet (FGURE 22). The roller 1114 pivots on the hinge pin d and may be securely fixed in any position of adjustment by the set screw 131.

When spinning at the rate of about 2.97 cubic centimeters of 0.8 percent collagen dispersion per minute, godet 1611 is preferably driven at a speed of about 10 rpm. At 10 rpm., the linear rate of spinning is about inches per minute. The spun strand passes twice around godet M11, the two loops being sufficient to preventl slippage.

Godet 1ll2 is preferably driven at 14 r.p.m. and therefore produces a percent stretch in the strand between godet 101 and godet 102. The amount of stretch at this stage may be increased or decreased as desired by varying the relationship between the speeds of godet 1(91 and godet 1&2. lt will be noted that the strand is wrapped around godet 102 twelve times (see FIGURE 23). This number of passes is usually required because the dry strand slips more easily. The stretching between godets 161 and 162 provides orientation of the drying strand and improves the tensile strength.

Spinning conditions may, for example, be controlled so that godet 101 is operated at 10 rpm., godet 102 is rotated at 14 rpm., and godet 103 at 15 r.p.m. Under these conditions, there is obtained, in addition to the 40 percent stretch between godets 101 and 102, another l0 percent stretch between godets 1112 and 103. The overall stretch may be varied from about 20 percent to 50 percent. Since the optimum amount of stretch will result in maximum strength, the machine is operated to give a stretch somewhat less than that required to break laments of the strand.

The moving filaments may be continuously washed and/or tanned at godet 101 or godet 102, or a two-step tanning procedure may be used by treating the filaments at godet 1111 and again at godet 1112. FIGURE 23 illustrates a method of contacting a united multillament by a downward flow of tanning solution in a direction opposite to the direction of thread travel. The wetted out thread returns from a freely rotating idler wheel 132 and contacts the tanning bath in a second stage. In its wet condition, the tanned thread is stretched an additional l0 percent by the more rapidly rotating godet 163.

The tanning solution is preferably circulated at the rate of 50 cubic centimeters per minute (25 cubic centimeters per minute through each jet). A suitable tanning bath may be made up by adding 4 milliliters of 40 percent queous formaldehyde and l gram of aluminum ammonium sulfate to l liter of water. The alumina arnmonia sulfate acts as a buffer and provides a pH of about 4.2. Two liters of this tanning bath solution may be recirculated without make-up, and will tan approximately 1000 feet of strand.

OneA problem that caused a great deal of difliculty was that of obtaining a strand having a circular cross-section. The multifilaments, as they emerge from the spin bath, are very loosely united and are approximately circular in cross-section; however, multiple passage over the circular godet surfaces, especialy when the filaments are under tension, forms a ribbon-like strand. This deformation taltes place most readily when the strand is wettest, as it leaves the spin bath and tanning bath.

The deformed strand from the godet may be rounded and dried by contact with a false twister of the type illustrated in FGURES 26 and 27. This device is constructed with a freely rotating idler wheel 5S and automatically imparts a so-called false twist to the strand, a false twist being a twist whose direction 0n one side of a point of contact is reversed on the opposite side, thus cancelling the twist. rl`he twisting cycle is most effective when the strand is in the wet state. When the twist backs up to the godet 1tl1, as the wet multitilaments emerge from it, a gradual tapering effect of the strand takes place, which rounds out. The circular shape of the strand remains after the twist is cancelled. The wringing action caused during the formation of the twist effectively dries the strand in a short space and reduces the tendency for the strand to break when subjected to stretch, thus permitting a large stretch betwen godets. To assist this drying action, a current of warm air from blowers 133 and 134 is preferably directed against the strand as it moves away from the false twister.

The false twisters are both operated in the range of to 1000 r.p.m. and may be driven by compressed air from the nozzle 57 against turbine blades 58 as shown in FIGURE 25. In the indirect spinning process, an open multifilament may be obtained if the multilarnent is not wet out in the bath 144, below godet 1l1 and the false twister is rotated at a low speed (about 2000 rpm.) to eect drying without uniting the individual filaments. ln the direct spinning process, the speed of the first false twister is such as to control the moisture in the strand to give the desired stretch (about 600 r.p.m.).

Referring ragain to FlGURE 9, it is important that the freely rotating roller 135, that precedes the false twister 113, be positioned in the machine about 44 inches above 11 the idler roller 16.5. This permits the wet tanned strand to dry out somewhat, and results in an improved circular cross-section. When the strand contacts the second false twister M3, it should be sufiiciently dry to avoid either deformation by the roller or reverse twist.

The tensiometers 3.42 and $.43 shown in FIGURE 9 measure tension placed on the dry strand by godets 162 and i013. The tension effected by the godet 192 varies from l to 300 grams with the humidity, temperature, speed of the false twister and other operating conditions. When the operating variables are well adjusted, it lis preferred to spin with a tension of between 75 and 150 grams.

The second stage tension on the dry strand effected by godet M3 is between 200 grams and 50()` grams. The dried strand is removed from godet E03 by the take-up spool, illustrated in FGURE 5, at approximately 45 inches per minute. The iinal strand, under the conditions described above, has ia diameter of about 6.5 mils (suture size 5/0).

lt has been observed that atmospheric humidity, a variable during the spinning of a strand, plays an important part in the stretch and the iinal tensile strength of the strand. The humidity is preferably controlled by encasing the spinning apparatus within the smallest practical enclosure into which air of controlled humidity may be introduced. Superior monolarnents are spun when the humidity is controlled between 30 and 60 grains of moisture per pound of dry air. Multifilaments may be spun when the humidity is less than 20 grains per pound. When the humidity is above 60 grains of moisture per pound of dry air, the filaments are soft and it is difficult to maintain the spinning tension.

it will be realized of course that although a vertically upward spinning process has been described above, the same principles will apply to vertically downward or horizontal spinning. Thus, with the spin bath in a horizontal position `as shown in FIGURE collagen dispersions may be spun with practically no modification of the operating conditions.

The direct spinning of a dispersion 0f swollen collagen fibrils to produce a unitary strand of outstanding properties will be illustrated by the examples, Examples I through IX. Throughout the specification, all quantities are expressed in parts by weight unless otherwise indicated.

EXAMPLE I Preparation of Collagen Dispersion That portion of the deep flexor tendon of cattle designated in FIGURE 2 as the D section is cleaned of fat, non-collagenous protein, and other extraneous matter, and is sliced on an electric meat-slicing machine (rotary knife) in the frozen condition. The tendon sections are sliced perpend-icularly to their longitudinal axis to a thickness `of about -25 mils.

The sliced tendon is next treated with an enzyme solution to dissolve elastin. The enzyme solution is prepared by agita-ting 240 parts of malt diastase with 2400 parts of water for l0 minutes. The homogeneous dispersion is centrifuged at 2000 rpm. for minutes, and the clear aqueous solution from the centrifuging step is vacuum filtered. The filtrate, which is usually slightly acid, is adjusted to pH 7 with a few drops of dilute sodium hydroxide. Distilled water is then added to the neutral enzyme solution to bring the total volume up to 7200 parts. Twenty-four hundred parts of the sliced tendon is immersed in this solution, which is then covered with a layer of toluene to prevent mold growth. rlhis tendonenzyme mixture is incubated at 37.5 C. overnight (l5- 20 hours).

After incubation, the tendon slices are washed 3 or 4 times by decantation with distilled water .and then treated with 6000 parts of water containing 4 grams of Versene (ethylene diamine tetrascdium tetraacctate). The tendon-Versenc iixture is incubated for approximately 2 hours at 37.5 C. to remove soluble proteins and lipids. Following this Versene treatment, the pH should again be adjusted to 7 if necessary as the tendon slices are easier to handle (less swelling and hydration) in a neutral solution. The tendon slices are again washed by decantation with 5 to 6 changes of rdistilled water.

The swelling solution is 50% aqueous methanol containing about 42.5%, based on the total solids weight, of cyanoacetic acid. In general, the collagen dispersion is easy to process at about 0.7% calculated solids concentration and the amount of acid-swelling solution may be readily calculated from the weight and solids content of the tendon used. The acid solution is prepared by mixing 44,604 parts of methanol with 42,169 parts of distilled water. To this aqueous methanol mixture is added 336.6 parts of cyanoacetic acid.

The acid aqueous methanol solution is cooled to below 25 C. and is added rto a dispersion kettle of suflicient capacity as illustrated in FIGURE 3, and the processed collagen slices are added to the dispersion kettle while rotating the stirrer at about 60 rpm. it is important that the remaining steps in the process be carried out at temperatures below 25 C. and that the temperature of the collagen dispersion not be allowed to exceed this temperature.

Stirring is continued for 3 hours, during which time the individual collagen slices are swollen. The dispersion is then homogenized by repeated passes through the stainless steel rotary metering pump 107 described above and the stainless steel series-connected jets (108 .and 109) having orifices of 30 mils and 40 mils. During the homogenization, the stirrer in the dispersion kettle is operated intermittently.

The pressure on lthe high pressure side of the homogenization jets falls to 70 pounds per square inch and remains constant after 3.5 hours, indicating substantially complete homogenization. The dispersion is then forced through 50- and 40-mil jets into a leaf filter containing 3 screens of #316 stainless steel. These screens are separated by 1x-inch spacers and decrease in mesh size so that the dispersion irst passes a 14mil screen, then a 9-mil screen and finally a 4-mil screen. During the filtration step, ythe pressure on the filter is maintained below 40 pounds per square inch at all times.

The dispersion of solvated collagen fibrils after filtration amounted to approximately 32,000 parts (0.68% solids). Six hundred parts of material is held up in the lter. The dispersion is an opaque, thixotropic mass which, at room temperature, `assumes a very viscous, slowly flowable state.

The dispersion of Example I may be dehydrated under mild conditions to recover highly purified collagen fibers. The dispersion may be extruded as described in subsequent examples to form collagen multitilament, tapes and strands.

EXAMPLE II Spinning the Collagen Dispersion (Direct Process) The collagen dispersion described in Example I above is deaerated under vacuum for 4 hours, aged for 3l hours at 25 C. and 16 hours at 5 C. and is then spun in the vertically upward spinning machine illustrated in FIG- URE 9. The pressure in the dispersion reservoir as indicated by the pressure gauge 141i is 15 pounds. The pump M5 is operated at 9.5 rpm. to extrude 2.82 milliliters of the dispersion each minute. The pressure at the filter as measured by the gauge H9 is approximately 10 pounds. The acetone dehydrating bath is continuously circulated to the spinning column at the rate of about 900 milliliters per minute. During this run, the ammonia content of the dehydrating bath is maintained at 13 138 milligrams per liter and the water content is 53 grams per liter.

The speed of the godets 101, 102 and 103 is maintained at 6.67, 9.00 and 9.33 rpm., respectively. rl'he false tWisters 112 and 113 `are both rotated at 600 r.p.m. The strand is continuously tanned at godet 102 by contacting an aqueous solution containing 4 milliliters of 40% aqueous formaldehyde and l gram of aluminum ammonium sulfate per liter, which solution is circulated at the rate of 50 cubic centimeters per minute (25 cubic centimeters per minute through each jet). The blower 133 is adjusted to maintain a tension of 45 to 50 grams as indicated by the tensiometer 142. The blower 134 is operated in a manner such that the tension indicated by the tensiometer 143 is about 190 grams. The relative humidity is maintained at 26% throughout the spinning.

The spinning machine operates continuously and Without any difficulties, such as broken strands or feathers under these conditions. The rate of take-up at the spool is about 42 inches per minute. At the end of 6 hours continuous spinning, `about 1300 linear feet of collagen strand (size 5/ 0, 244 denier), is collected.

Random samples are cut from `different sections of this continuous strand. Each sample is 5 `feet in length. These samples are packaged in tubes containing 90% isopropyl mcohol and Water by volume and the samples sterilized by elcctron beam irradiation (3 105 reps). The straight tensile strength (dry) and knot strength both wet and dry) for these sterile samples is reported in rlable 1.

In Table l, the dry straight tensile strength (6 breaks reported in pounds) is given in column 1. The dry knot tensile strengths (7 breaks reported -in pounds) is given in column 2. The wet knot tensile strength (5 breaks reported in pounds) is given in column 3. The Wet knot tensile strength is measured by immers-ing a strand about 1 foot in length in distilled Water for 5 minutes, tying a knot near the center of the strand and lbreaking the strand at the knot. Column 4 gives the papain digestion time. This is the time in hours required for a 7-inch strand tied to form a loop to go to` gram strength at 38 C. in -a solution of papain containing 3 grams of the enzyme in 100 milliliters of a buffered solution containing 7.6 grams of thiourea. Four milliliters of 5% sodium cyanide are added to 96 milliliters of fthe above buttered solution of papuin just prior to use. rI'he nal pH of this solution is 7.2. Column 5 gives lthe hot Water digestion time. This is the time in minutes required for a 7-inch strand, :tied to form a loop, to go to 20 grams strength at 100 C. when immersed in a solution of water buttered at a pH of 1.35.

From Table 1, it may be calculated that the average ry straight tensile strength is 2.00 pounds. The average dry knot tensile Strength is 1.27 pounds. The average wet knot tensile strength is 0.95 pound. These values correspond to a dry straight tensile strength of 3.72 grams per denier, a dry knot tensile strength of 2.36 grams per denier and a wet knot tensile strength of 1.79 grams per denier.

EXAMPLE llll The collagen dispersion of Example l, after aging for 24 hours at room Itemperature and 47 hours at 5 C. is spun by the process described in Example II above. The pump speed is 8.5 rpm., and the concentration of ammonia and water in one liter of the acetone bath is 130 milligrams and 51 grams, respectively. The flow rate of the acetone bath is 900 cubic centimeters per minute. The godets are operated at 6.7, 9.0 and 9.3 r.p.m. The false twisters are both operated at 600 r.p.m. The vformaldehyde tanning bath of Example 1I is used and the tension preceding godets 102 and 103 is 68 grams and 190 grams, respectively. Under these conditions, .the sterile strand (denier of 217) has a dry knot tensile strength of 3.05 grams per denier and `a Wet knot tensile strength of 2.17 grams per denier.

EXAMPLE 1V The dispersion `of Example I, after aging 88 hours at room temperature and 448 hours `at 5 C. is spun by the process described in Example II. The laments are, however, wet out with a Achromium tanning solution in the bath 144 below godet 101, as illustrated in FIGURE 2l.

A chromium stock solution is prepared by dissolving a mixture of 17.1 mill-ililters of concentrated sulfuric acid, 51.1 grams of potassium dichromate, and grams of sodium metabisulte in Water. This solution is made up to 1 liter of stock solution with Water. The stock solution analyzes 27.6 lmilligrams of chromium per milliliter.

The chromium tanning solution used in bath 144 is made up by diluting 25 milliliters of the chromium stock solution with distilled Water to a total Volume of milliliters. The pH of the chromium tanning solution is about 3.7. The yformaldehyde tanning bath described in Example 1I is used between godet 102 and godet 103. The spinning conditions are as follows:

godet 102; 160 grams before godet 103.

The strand so obtained is sterilized as described in Example Il. Randon 5-oot lengths (denier of 252) are tested for wot straight tensile strength and average 2.88

-grams per denier.

The papain digestion times, as determined by the test `described in Example l above, is 3.5, 2.9, 4.0, 2.9 and 3.2 hours on fthe 5-random samples.

The hot water digestion time, as determined by the test described in Example 11, is 5.7, 5.7 and 5.7 minutes on three random samples.

Other random samples of this product (denier of 252) have a dry straight tensile strength of 4.3 grams per denier, a dry knot tensile strength of 2.2 grams per denier and n Wet knot tensile strength of 1.9 grams per denier.

The dry tensile strength in pounds on 7 random samples of this product is 2.50, 2.55, 2.28, 2.33, 2.35, 2.40 and 2.44. The average is 2.41 pounds and the variation is 0.27 pound (i5.5%).

EXAMPLE V The dispersion of Example l is aged for 173 hours at room temperature and 43 hours at 5 C., and is spun by 

1. IN THE METHOD OF PRODUCING A COLLAGEN STRAND, THE STEPS OF EXTRUDING A HOMOGENOUS DISPERSION OF SWOLLEN COLLAGEN FIBRILS THROUGH A STATIONARY SPINNERETTE TO FORM A MULTIFILAMENT; APPLYING A WATER-MISCIBLE ORGANIC LIQUID DEHYDRATING AGENT MORE VOLATILE THAN WATER TO SAID MULTIFILAMENT; STRETCHING AND TWISTING SAID MULTIFILAMENT WHILE EVAPORATING THE ORGANIC LIQUID WHEREBY THE MULTIFILAMENT UNITIES TO FORM A STRAND; AND DRYING SAID STRAND. 